A tape driving system of a magnetic recording and/or reproducing apparatus must accurately move the magnetic tape along a lead provided on a drum to maintain linearity of video tracks. For this purpose, flanges are provided on the tape guides arranged on both sides of the drum. The tape can be moved along the lead on the drum, with the tape being disposed between the upper flange and the lead. Further, another flange is provided on each of the other tape guides between a supply reel and take-up reel in a cassette to govern the tape driving height. This makes the tape move along the lead on the drum easily and at a higher accuracy.
On the other hand, the tape stiffness decreases as the tape thickness is reduced and surface friction coefficient of the tape is increased as the surface characteristics of the tape are improved.
In a conventional magnetic recording and/or reproducing apparatus, the flange of the tape guide has a surface perpendicular to a cylinder axis of the tape guide which governs the tape driving height. An apparatus of the above-noted type is described in, for example, Japanese Patent Application Laid-Open 61-233452. However, with the tape height governed by the planar surface perpendicular to the guide, edges of the tape guided by the flange are deformed or bent, thereby resulting in damage to the tape edges. This is due to the low stiffness of the tape and difference of the flange planar surface from the tape running direction. If, for example, the tape guide is a revolving roller type, the tape may be largely moved up or down even with a slight deviation of the roller revolution direction from the tape running direction, thereby resulting in a large deformation. One of the causes of such a phenomenon is the guiding of the flange on the tape edges even in the area of the tape which is not round on the tape guide as the flange planar surface is larger than the tape guide diameter. The tape is deformed along that area. To avoid this, it has been proposed to conically shape the flange with a small taper angle, so that the height is governed only by a portion on which the tape was wound. It has also been proposed to fix the tape guide so that the guide is not rotatable, with a spacer or the like being inserted between the tape guide and the flange in a direction from a side opposite the side having the tape wound, thereby resulting in a slanting of the flange. With the flange being slanted, the height is governed only on the portion having the tape wound and at the same time, the governing or controlling force is stronger on the center portion of the tape winding and weaker as the tape nears its entrance or exit to prevent deformation of the tape.
In the conical flange construction of the prior art, the flange for governing or controlling the height is parallel to the tape. For this reason, it is difficult for the flange to completely govern or control the tape for parallel movement if the tape guide and the like deviate in accuracy or if the tape running height is deviated. The governing or controlling force tends to be too high in a vicinity of the entrance and exit of the tape winding. That is, the prior art has the disadvantage that the tape is deformed due to the low stiffness of the tape.
In the slant flange construction of the prior art, the tape guide increases a running load of the tape since the tape guide is fixed. This construction has the disadvantage that the thin tape is damaged, or contact of the tape with the head is deteriorated. With the spacer insert, the thickness of the spacer must be determined to prevent the tape from being deformed with respect to accuracy deviation of the tape guide and change of the tape running position due to variation of the tape tension. In this connection, the prior art construction has the problem that, with the insertion of the spacer, it is difficult to control the slant angle of the flange with a high accuracy. Furthermore, if the spacer of a predetermined thickness fails to prevent the tape deformation, the spacer must be replaced by a spacer of a different thickness. Additionally, the running height has to be unnecessarily governed or controlled in the vicinity of the center portion of the tape winding in dependence upon the accuracy of the running path of the tape. If the tape is run for a long period of time or at a high speed in that state, friction of the tape with the flange generates heat, thereby resulting in tape damage.